Calculating and tuning compound turbos...
 

For those of you running multiple turbo setups...

Does anyone have some equations or methodology as to choosing the right combination of turbos, and how to tune them???

I'm looking into building a compound setup in my truck, but I'd like to crunch some numbers first to make sure that I choose the right setup for my needs. My rig is a daily driver with occasional trailer towing duty, so I would like a cool and reliable 500 hp (which is like EVERYONE's generic first target, right? :tttt:) Just to dismiss any concerns, I am fully equipped with gauges and have a fortified NV4500 waiting to go in when I start working over the engine (again :argh:) for the dual spinny things. My current 'charger is a Phatshaft 62/71/14.

Any techno jargens will be greatly appreciated so I can design this setup properly and avoid as many of the dreaded "trial and error" flops as I've sadly grown accustomed to by "blind bombing"... Oh how we silly kids are so ambitious to fail :argh:

Thanks!

just put a S475/96/1.32T6 under your S362/71/14T3 and you should be fine that would support upwards of 750hp, if your only planning on 500 then a S471/96/1.32T6 would work also (thats what BD uses in their small set)

shouldnt have any drive pressure issues with that setup

I've got a spreadsheet made up that helps to calculate airflow requirements at different RPMs at wide open throttle. It is still incomplete, but you need the compressor maps for both turbo to compare to once you get your airflow requirements. My spreadsheet included the temperature rise and density calculation for increased accuracy, but essentially you need to decide the pressure ratio you want to run on both turbos.

Pressure ratio is basically the amount the compressor will multiply the pressure at the inlet. So if you have 1bar(sea level) at the compressor inlet, and you want a ratio of 2:1, you will see 1bar(subtract the atmosphere pressure at the inlet) at the gauge for boost. So if you wanted to run 2:1 on your low pressure turbo as well you would see 3bar at the gauge. That works out to 2bar at the LP inlet, multiplied by 2 minus atmosphere pressure.

There is a really good book that has the formulas in it, I'm on my iPhone and out of town so I cannot referense the material at this time. The book is called "Turbocharging" by Hugh Macinnes.